Methods for producing carboxylic acid by oxidation of alcohol with nitric acid (Org. Synth., 5, 9–11, Org Synth., Coll. Vol. 1, 18–20, Compt. Rend., 1919, 168, 1324–1326, J. Chem. Soc., 1942, 559–562, J. Chem. Soc., Perkin Trans. II, 1985, 1677–1682), chromic acid (Org. Synth., Coll. Vol. 4, 19–21), potassium permanganate (Chem. Ber., 1908, 41, 575, Chem. Ber., 1922, 55B, 3526–3536) have been reported. However, it is hard to say that these methods are industrially superior processes because of the large load on the environment in terms of the generation of by-products having high toxicity, corrosiveness of the oxidizing agents, and the like.
On the other hand, oxygen and hydrogen peroxide are excellent oxidizing agents in industrially applying them due to small environmental load, because they are inexpensive and have no corrosiveness, and there is no by-product after the reaction or it is harmless water.
As a method for producing carboxylic acid from alcohol by using oxygen as the oxidizing agent, a method using a platinum-supported catalyst has been already proposed (Appl. Cat. A, 1996, 135, L7-L11).
However, this method must be carried out under pressurization of oxygen at a high reaction temperature (150° C. or more) and, in addition, selectivity of the obtained carboxylic acid is as low as merely about 50%.
On the other hand, methods for obtaining carboxylic acid by using hydrogen peroxide as the oxidizing agent include a method in which a homogeneous solution of cyclohexanol and hydrogen peroxide is prepared in advance by using a polar solvent, and adipic acid is produced by allowing this homogeneous solution to react in the presence of a catalyst such as a metal oxide belonging to Group 6 of the Periodic Table has been proposed (JP-A-54-135720).
However, it cannot be said yet that this method is sufficient as an industrial carboxylic acid production method, because the yield of adipic acid by the method is considered to be merely about 50%, and it is essential to use a polar solvent such as acetic acid or t-butyl alcohol for preparing a homogeneous solution by dissolving cyclohexanol in an aqueous hydrogen peroxide, so that the reaction operation and apparatus become complex because of the necessity to employ a means for its removal at the time of the isolation of adipic acid as the product of interest, in addition to the indication on the influence and toxicity of the polar organic solvent itself upon the environment and human body.
In addition, in the method for producing carboxylic acid by oxidation of ketone, nitric acid is used as the oxidizing agent (Chem. Ber., 1894, 27, 1542–1546), but this method has a high possibility of causing explosion during the reaction and nitrogen oxide which is a toxic gas is produced as a by-product after the reaction. The reaction using potassium permanganate as the oxidizing agent (J. Chem. Soc., 1956, 4232–4237) requires treatment after the reaction using sulfuric acid, and the operation is dangerous and complex. A method is known in which chromic acid (Helv. Chim. Acta, 1948, 31, 422–426, J. Am. Chem. Soc., 1967, 89, 6691-6695) or potassium superoxide (Tetrahedron Lett., 1978, 3689–3690) is used as the oxidizing agent in the presence of sulfuric acid or perchloric acid, but there are problems in these reactions such as corrosiveness of the oxidizing agent and the use of an acid or a benzene solvent. It is hard to say that these methods for producing carboxylic acid from ketone are industrially superior methods because of the large load on the environment.
On the other hand, oxygen and hydrogen peroxide are excellent oxidizing agents in industrially applying them due to small environmental load, because they are inexpensive and have no corrosiveness, and there is no by-product after the reaction or it is harmless water.
Methods for producing carboxylic acid from ketone by using oxygen as the oxidizing agent are already known (Chem. Ber., 1892, 25, 1271–1277, Chem. Ber., 1892, 25, 2095–2102, J. Chem. Soc., 1909, 95, 166–171, J. Org. Chem., 1965, 30, 3768–3771), but large excess of a strong base based on the substrate is necessary in these methods. Also, formation of carboxylic acid from ketone by using oxygen as the oxidizing agent in the presence of a metal catalyst such as a manganese or cobalt salt has been reported (U.S. Pat. No. 2,005,183 specification, U.S. Pat. No. 2,316,548 specification, JP-A-13-213841, WOP 2001-87815 specification), but carboxylic acid is not obtained by these methods unless acetic acid is used at a solvent amount. In addition, when aerobic oxidation is carried out by using an iron or vanadium catalyst (J. Org. Chem., 1983, 48, 1133–1135, J. Org. Chem., 1993, 58, 5663–5665), the conversion ratio is low unless an electron donating substituent group is linked to the α-position of the ketone. Moreover, a benzene solvent is necessary for the reaction when the iron catalyst is used.
On the other hand, as a method for obtaining carboxylic acid by using hydrogen peroxide as the oxidizing agent, a method using a catalytic amount of a metal compound belonging to Group 3 or Group 13 of the Periodic Table has been proposed (WOP 2000-53593 specification), but the product obtained by this method is not carboxylic acid but an ester or lactone compound.
In addition, a method in which a homogeneous solution of cyclohexanone and hydrogen peroxide is prepared in advance by using a polar solvent, and adipic acid is produced by allowing this homogeneous solution to react in the presence of a catalyst such as of a metal oxide belonging to Group 6 of the Periodic Table has been proposed (JP-A-54-135720).
However, it cannot be said yet that the method is sufficient as an industrial carboxylic acid production method, because the yield of adipic acid by this method is considered to be merely about 50%, and it is essential to use a polar solvent such as acetic acid or t-butyl alcohol for preparing a homogeneous solution by dissolving cyclohexanone in an aqueous hydrogen peroxide, so that the reaction operation and apparatus become complex because of the necessity to employ a means for its removal at the time of the isolation of adipic acid as the product of interest, in addition to the indication on the influence and toxicity of the polar organic solvent itself upon the environment and human body.